This invention relates to a railroad sleeper lock-in shoulder and further to such a shoulder when associated with a sleeper rail and fastener to form an assembly to fasten a pair of rails to a sleeper. In our Australian patent application No. 83610/82 lodged on May 12, 1982 and published July 25, 1983 there was described and claimed a resilient fastener clip of general "U" shape arranged to have its upper leg bearing upwardly against the head of a "T" head restraining member, its heel bearing downwardly and against the sleeper and its lower toe bearing downwardly against the rail foot. Clips made in accordance with that invention have proved to be technically successful, and this invention is associated with certain improvements wherein such a clip can be used in conjunction with the shoulder which can be locked into an aperture in the sleeper by the rail foot itself.
There are many advantages in the use of a "knock-on" clip, as distinct from clips secured, for example, by screw threaded fasteners. The "knock-on" clip has such a shape that rail vibration will return it to its required position (if displaced). A "knock-on" clip of the type described herein has an excellent spring rate, which will tolerate settlement of a rail pad formed from polymeric material, with only slight loss of rail foot pressure. It will resist rail creep better than any known type of other fastener clip. It is easily assembled to a rail, and although it resists dislodgement, for example by vandals, it can be easily removed with an appropriate tool. It has a low profile and will allow free movement of a rail track machine, offering little or no obstruction. Above all, in use its failure rate is negligible.
However its use normally requires the addition of a "T" headed stud welded to the upper surface of a sleeper. In many instances it is much preferred to drill a hole in a sleeper, and the main object of this invention is to provide a successful lock-in shoulder which can be used in conjunction with such a configuration.
Lock-in shoulders have been proposed heretofore, and for example the reader's attention is drawn to British specification No. 1,434,560 directed to a three-part fastener (shoulder, clip and retaining pin). U.S. Pat. No. 3,442,452 discloses a "U" shaped clip which engages a cast-in shoulder or retention member embodied in concrete. U.S. specification No. 3,356,299 Boyer discloses a lock-in clip with a screw threaded fastener bearing downwardly on a rail foot in such a way that there is a large unlocking moment tending to rotate the clip out of its retaining slot. However, the most pertinent prior art known to the Applicant is to be found in U.S. specification No. 2,085,970 Greene which shows a lock-in sleeper having a foot which bears upwardly against the under surface of a sleeper, and is retained in that position by a spring clip. However, there is an inherent instability in the arrangement shown, for example, in FIG. 3 of the Greene drawing. If moments are taken about the uppermost point where the lock-in block contacts the rail foot, it will be seen that clockwise rotation is inhibited solely by the depressed portion of the clip (near its heel) contacting a surface (4) of the sleeper. However, the direction of possible rotation is such that the contact is oblique, not "square-on". Lateral forces imparted by the rail foot will not correct this anomaly.